Regardless of the huge advances made in the design and fabrication of
mid-infrared and terahertz quantum cascade lasers, success in accessing the
~3-4 mm region of the electromagnetic spectrum has remained limited. This
fact has brought about the need to exploit resonant intersubband transitions
as powerful nonlinear oscillators, consequently enabling the occurrence of
large nonlinear optical susceptibilities as a means of reaching desired
wavelengths. In this work, we present a computational model developed for the
optimization of second-order optical nonlinearities in
In0.53Ga0.47As/Al0.48In0.52As quantum cascade laser structures based on the
implementation of the Genetic algorithm. The carrier transport and the power
output of the structure were calculated by self-consistent solutions to the
system of rate equations for carriers and photons. Both stimulated and
simultaneous double-photon absorption processes occurring between the second
harmonic generation-relevant levels are incorporated into rate equations and
the material-dependent effective mass and band non-parabolicity are taken
into account, as well. The developed method is quite general and can be
applied to any higher order effect which requires the inclusion of the photon
density equation.
Photon-induced carrier transport in high efficiency midinfrared quantum cascade lasers